1. Field of the Invention
This invention relates to a target identifying apparatus, a target identifying method, and a target identifying program for identifying from a signal distribution with beam angle or frequency provided by a scan radar as a parameter, a target contained in the signal distribution.
2. Description of the Related Art
Hitherto, a on-vehicle radar sensor installed, which is a scan radar of FM-CW for emitting a continuous transmission signal frequency-modulated with a triangular wave and receiving a reflected wave from a target (another vehicle ahead of the vehicle) for each beam angle as a reception signal, thereby calculating a direction angle of the target, distance to the target, and relative speed between the radar sensor and the target has been available as shown in FIG. 2A.
The calculation method will be briefly discussed. In the scan radar, a signal distribution with beam angles used as a parameter in which power of a reception signal is distributed for each beam angle is generated as shown in FIG. 2B. The direction angle of the target is calculated from the signal distribution. The transmission signal is mixed with the reception signal to find a beat signal for each beam angle. Then, the beat signal is subjected to fast Fourier transform (FFT) for each beam angle. In a rising section and a falling section for each beam angle, a signal distribution with frequencies used as a parameter in which the power of the beat signal is distributed for each frequency is generated as shown in FIG. 10B. The distance to the target and the relative speed between the radar and the target are calculated from the signal distribution (peak frequency) in the rising section and the signal distribution (peak frequency) in the falling section.
Thus, in the scan radar, the direction angle of the target, the distance to the target, and the relative speed between the radar and the target are calculated from the signal distributions with beam angles and frequencies used as the parameter. For example, if a plurality of targets are close to each other in the left and right direction as shown in FIG. 2A, a peak (signal) for each target does not clearly appear in the signal distribution as shown in FIG. 2C. To solve this problem, measures for narrowing a beam width of an antenna for shortening sampling intervals (beam angle intervals), thereby clearly forming a plurality of peaks in the signal distribution has been conceived. However, if a beam width of an antenna is narrowed, new problems occur. That is, since an area of the antenna is enlarged, size of the radar becomes large. Also, since number of beams increases, processing load increases.
Thus, hitherto, it has been a general practice to use an art of applying an antenna pattern (antenna application pattern) to a signal distribution in which a peak for each target does not clearly appear as disclosed in JP-A-2002-14165. That is, as shown in FIG. 11A, the antenna pattern is matched with the signal distribution, thereby removing a side lobe component from the signal distribution to generate a new signal distribution as shown in FIG. 11B. The presence of a target is identified from the newly generated signal distribution and then, the direction angle of the identified target is calculated.